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wiring a NEMA 6-15R for a Delta Unisaw

skozub's picture

I recently got my new Delta Unisaw (3hp 230 volt) home to the shop only to discover that Delta had a unique plug on the end of the cord. I spoke with Delta and they confirmed that the plug was a NEMA 6-15P and that I needed to go buy a NEMA 6-15R (single receptacle) so I could rewire the outlet for the plug.

I had a certified electrician wire the shop months ago for this service. He installed a 30 amp breaker with the appropriate gauge wire (#8 or #10 I think) and wired a 250 volt, 30 amp receptacle with the twist lock. these are the kind you can buy at Home Depot. Problem is, Delta's saw isn't set up for that and I can't change the cord configuration or bye-bye warranty.

Now I have the NEMA 6-15R in the wall and the saw works, but I'm not sure I re-wired things correctly. Since it's 220 volt service I have two hots, one neutral and one ground running to the outlet. My original electrician wired the two hots to the 30 amp 250 volt receptacle (noted above) and put the neutral into the ground slot. So I did the same with the new receptacle. However, I'm not 100% sure this is correct b/c now I have a ground line that's just sitting inside of the box with nothing to do. I don't have any more places to stick I tie the neutral wire or the ground wire to the ground screw? Which one sits loose inside of the box?


John_D's picture

(post #115986, reply #1 of 15)

When you say replugging will void your warranty, what makes you say that?

I know, for example, that my 5HP Unisaw came with a plug, which was definitely not the right size.  I replaced this plug and the lightweight wire to which it was attached, with a NEMA 6-30, matching the plugs in my shop.  I've also put NEMA 6-30's on my jointer and bandsaw.  All the machines' instructions had directions on re-plugging.

Machinery isn't really like a Nintendo or a Sony box.  It's very normal to have to do this terribly minor sort of alteration.  I simply do not believe you are endangering your warranty by re-plugging.  Just make sure you use a plug and wiring suitable to your saw.

Anyway, you've gone down another road.  There should not be a neutral at all.  Some appliances (typically, old dryers) use both 220 and 110 -- this is the reason for a neutral in a 220 circuit -- but a standard 220v circuit has two hots and a ground ONLY.

I'd say you should seal off the neutral, and use the ground, but who knows what he did at the other end or along the way?  If you can't get him to come back and make good, and if you don't have the knowledge to check it yourself, personally I'd have another electrician check it out.  You can't tell if you've got a good ground by whether the saw works, and a good ground is critical for shop safety.

And before someone says it, yes, of course neutral is typically bonded to ground back at hte box, but doing it right is worthwhile.  What the electrician did is sloppy at best.

My goal is for my work to outlast me.  Expect my joinery to get simpler as time goes by.
My goal is for my work to outlast me.  Expect my joinery to get simpler as time goes by.
skozub's picture

(post #115986, reply #4 of 15)

Excellent. Thank you gentlemen.

I too thought I could re-plug the line, but the two Delta reps I spoke with said if I did my warranty was null and void. Perhaps they are incorrect. I've had to plug all of my other tools so far (jointer, bandsaw, planner) without issue but Delta is the only one who provided a plug (and a funky one at that).

I will disconnect the white 'neutral' wire and tape it off with a nut, and reconnect the bare cooper ground wire. I greatly appreciate the insight.

These comments have been consistent with electrical diagrams I found online for the exact receptacle I purchased. Thanks for keeping us safe and out of harm's way.

TKanzler's picture

(post #115986, reply #5 of 15)

Your 3 hp Unisaw is a UL listed appliance, and as such, it came with a cord and cap (plug).  Cutting the plug off our television set to plug it into a 30A 120V circuit would give Sony fits, too, if you brought it in for a warranty repair.  Changing the plug may not have anything to do with what went wrong, but that, I'm sure, is what Delta's hanging their hat on.  The NEC also requires installation instructions to be followed, which in your case probably means a 240V 20A circuit.  It has to do with the ability of the equipment to handle a short-circuit or ground-fault within the equipment itself without starting a fire or worse - it's the same reason UL won't list a table lamp with 22 gauge wiring and a 30A plug.

The 6-15 configuration is 240V 15A, and the plug will fit a 240V 20A receptacle, just like a 120V 15A plug fits a 120V 20A receptacle.  If you changed the receptacle to a 6-15 or 6-20, you need to change the breaker to a 15A or 20A respectively, if it's the only receptacle on the circuit, which it sounds like it is.  That's if you want the installation to conform to the NEC. 

You also need to use the ground, not the neutral, as mentioned above.  The neutral is at the same potential as the ground only if there is no current flowing on it, and if the neutral comes from a subpanel, the bus in the subpanel will be flowing current, so the neutral will not be at zero volts (compared to the connection in the service equipment, usually the main panel).  That's why the grounds and neutrals are isolated in a subpanel, and why you don't want to use a neutral as a ground if it comes from a subpanel.  If you want to be NEC compliant, don't use a neutral for a ground at all (except for grandfathered range and clothes dryer installations - new ones are 4-wire only).

Be seeing you...

Be seeing you...

skozub's picture

(post #115986, reply #6 of 15)

Thanks.  All of the lines come from the main panel.  I had the main panel dropped into my shop where all electricity runs directly from for the shop. There is a sub-panel in the main that connects to the house.

BarryO's picture

(post #115986, reply #9 of 15)


That has got to be the best electrically-related posting I've read in a long time...

fuzzyface's picture

(post #115986, reply #10 of 15)

I believe current (no pun intended)electrical codes require a 4-prong plug on 220 volt lines, two hot, neutral and ground. The receptical slots are also shaped different than the old 3-prong 220 recepitals. Mufacturers will generally refuse to change the 4-prong cord to the older type because of liability, but it is perfectly allowable, and legal, for the purchaser to make that change.

All new clothes dryers and electric stoves now come with the 4-prong plug, but if your house was built more than five years ago it will have only the 3-prong outlets. Putting the old (or buying a new 3-prong cord ) on the new dryer, stove, or workshop machine, is cheaper than rewiring the circuit.

John_D's picture

(post #115986, reply #11 of 15)

220 lines, such as one would install to feed a table saw or other woodworking machinery, do not have a neutral.  Typical examples are NEMA 6-30, 6-30L and 6-50.

You're thinking of 220/110 outlets, such as those used by some washers and dryers (they use 220 for the motor and heater, 110 for the light bulb); these (like the NEMA 10-50) had two hots and a neutral (you get 110 off one hot and the neutral, 220 off the two hots), and there was no ground at all.  The lack of ground is why new installations do not use this connector; instead, the NEMA 14-50 is used, which adds a grounding connector.  If you buy an appliance with a 14-50, you'd be well advised to rewire the NEMA 10-50 by adding a true ground, and converting to a 14-50.

General-purpose connectors for 220v operation (such as NEMA 6-30 and 6-50 etc.) contain three conductors:  hot, hot, and ground.  There is no use for a neutral in a 220 circuit, and none exists.

My goal is for my work to outlast me.  Expect my joinery to get simpler as time goes by.
My goal is for my work to outlast me.  Expect my joinery to get simpler as time goes by.
BarryO's picture

(post #115986, reply #12 of 15)

I believe current (no pun intended)electrical codes require a 4-prong plug on 220 volt lines, two hot, neutral and ground.

No.  Receptacles supplying 240V are 3-wire:  two Line ("hot") conductors, and an Equipment Grounding Conductor ("ground").  This is the type of branch circuit used by power tools.

Electric clothes dryers and stoves are not supplied by 240V circuits, but rather by 120V/240V multiwire branch circuits.  You are correct in that receptacles used on these circuits are 4-wire:  two Line Conductors, an Equipment Grounding Conductor ("ground"), and a Grounded Conductor ("neutral").

Older 120V/240V branch circuits for dryers and stoves used nongrounding, 3-wire receptacles:  two "hots" and one "neutral".  This type of receptacle may be found in older installations, and it is permissible under the Code to install new equipment with a plug that matches this type of receptacle.  But it is not permissable to install new circuits of this type.

Edited 4/12/2006 6:39 pm by BarryO

JohnWW's picture

(post #115986, reply #2 of 15)

You could have changed the plug without voiding the warranty unless Delta was being extremely cranky about it.  Most machines that size don't even come with plugs and expect that the purchaser will supply the plug, and often times the cord, that they prefer.

Neutral and ground are electrically identical when everything is going well so having the neutral connected to a ground terminal won't cause an immediate problem, and the saw will run properly, but it is unsafe and violates code to have things wired the way you describe.  If your electrician did this he should find another line of work.

Just to be sure you are identifying the wires properly, the red and the black leads are supposed to be the hot wires, the white wire is the neutral, and the ground will either be bare copper or have green insulation.

The proper connections would be the two hot leads and the ground wire are connected to the appropriate terminals on the receptacle and the neutral wire is left disconnected, but capped with a wire nut in the box.  If the box is metal, it should also be connected to the ground wire.

John W.

John White Shop Manager for FWW Magazine, 1998 to 2007

Piccioni's picture

(post #115986, reply #3 of 15)

Neutral should be a no connect. You have 3 prongs: Hot, Hot, and Ground.

Neutral is generally used on a 220 volt outlet when the ability to feed 110 is also needed.

gb93433's picture

(post #115986, reply #7 of 15)

Many new homes and machines today have a 4 wire service: 2 hots, one cold and a ground.

porthios's picture

(post #115986, reply #8 of 15)

probly a bit too late to help you but when i got my new unisaw home i ran into the same problem. i just made up a small extension cord with the appropriate plugs and receptacles at either end to match the delta plug and my in wall receptacle.

the delta cord reaches just about to the end of the extension table anyway and that make it very convenient to unplug the saw for changing blades etc..

enjoy the new saw ;)

HowardAcheson's picture

(post #115986, reply #13 of 15)

Before we beat up on the electrician, we should ba aware that he probably did the correct thing.  Unless he was told exactly what the circuit was being wire for, he would have naturally gone with a 30 amp, 4 wire, dual voltage circuit using #10 AWG wire.  That way, no matter what the final configuation turns out to be, there is wiring that can handle it.  A dual voltage circuit (120/240) requires four wires under current code.  Two hots, a neutral and a ground.  That way, a dual voltage appliance such as a clothes drier, could be used without having to pull another wire. 

To wire for the Unisaw, all that is necessary is to replace the existing receptacle with a receptacle that matches the plug and then install the proper amperage breaker.  In this case, the white wire is capped off and only the two hots and the neutral wired to the 15 amp receptacle (perfectly normal and within code).  Then the breaker MUST be changed to a 15 amp--not 20 amp) breaker.

user-5900479's picture

Very helpful, but regarding breakers... (post #115986, reply #14 of 15)

Very helpful thread. I'm in a very similar situation 220V 6amp belt sander with a 6-15 male plug, 50amp receptacle and breaker.

But I can't change the breaker or do any hard wiring, I have to work with the 6-50 3 pin (2 straight blades, 1 u-shape pin) receptacle.

Is there any cheap way, without buying a spider box, that I could reduce amperage between the 6-50 receptacle and the tool? What might such a thing be called? inline breaker? that I could hardwire into the cord? or an adapter?

PS: I'm not too knowledeable about the nitty gritty ofg electricity (don't understand phases, etc.), so go easy on me. 



leminhtien's picture

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